Why do pro gay marriage people see people that are Anti Gay Marriage as ignorant?

I myself am a Christian. And in being a Christian I don’t support gay marriage one bit. Why do pro gay marriage people think Anti-gay marriage people are “ignorant,” and or brand us “gay?”

I’m not gay. I just don’t see it as something that should be legalized. I mean think about it. If we grant gay marriage, then why don’t we let a 49 year old guy have sex with a three year old? It’s the same thing. Once you open a door for one thing, you have to let all things in. I mean the man that wants to have sex with the three year old needs his rights too, right? Or what about a mom that wants to have kids with her son? Does anyone see what I am aiming at??